docs: update Learning Hub for Copilot CLI v1.0.37–v1.0.40 changes (#1610)

- automating-with-hooks.md: Add prompt mode security gate note (v1.0.40)
  — repo hooks and workspace MCP are disabled by default in -p prompt mode;
    users must opt in via GITHUB_COPILOT_PROMPT_MODE_REPO_HOOKS and
    GITHUB_COPILOT_PROMPT_MODE_WORKSPACE_MCP env vars

- agents-and-subagents.md: Add /research orchestrator/subagent note (v1.0.40)
  and prompt mode security cross-reference for /fleet -p examples

- building-custom-agents.md: Document ACP agent list/switch capability (v1.0.40)
  — ACP clients can now list and switch custom agents via agent config option

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/content/docs/learning-hub/agents-and-subagents.md

@@ -3,7 +3,7 @@ title: 'Agents and Subagents'
 description: 'Learn how delegated subagents differ from primary agents, when to use them, and how to launch them in VS Code and Copilot CLI.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-04-02
+lastUpdated: 2026-05-04
 estimatedReadingTime: '9 minutes'
 tags:
   - agents
@@ -123,6 +123,8 @@ For non-interactive execution:
 copilot -p "/fleet Update the auth docs, refactor the auth service, and add related tests." --no-ask-user
 ```
 
+> **Prompt mode and repo hooks (v1.0.40+)**: When using `copilot -p "..."` (prompt mode), repository hooks are disabled by default for security. If your `/fleet` workflow relies on hooks (e.g., auto-formatting or lint checks after edits), opt in by setting `GITHUB_COPILOT_PROMPT_MODE_REPO_HOOKS=true` before running. See [Automating with Hooks](../automating-with-hooks/) for details.
+
 The important behavior is different from a single chat turn:
 
 - the orchestrator plans work items first
@@ -146,6 +148,8 @@ Run parallel subagents for different lenses - correctness, security, code qualit
 
 Use one subagent to gather facts and another to implement with those facts. This pattern is especially helpful when you want the main thread to stay free of exploratory noise.
 
+The built-in **`/research`** command uses this orchestrator/subagent model automatically (v1.0.40+): it spawns an orchestrator that breaks the topic into research threads, runs them in parallel as subagents, and synthesizes the findings into a structured report. This means you get deeper and more reliable results than a single-turn query provides — without having to set up the multi-agent pattern yourself.
+
 ## Repository examples you can inspect
 
 This repository already includes a few useful examples of delegation-related syntax: